There are few general theories of international relations. One reason for this may be its relatively late emergence as a field of study. The first department and chair of international relations – both at the University of Wales in Aberystwyth – were established only in 1919. More fundamentally, the nature of the subject inhibits theoretical development. International relations is at the apex of multiple levels of social aggregation, and is significantly influenced, if not shaped, by what happens at other levels. A good theory of international relations presupposes a good understanding of politics at all these other levels. It would be something akin to a unified field theory in physics. Einstein devoted his mature decades to this goal, and failed, as anyone would in the absence of more knowledge about the individual forces that have to be subsumed by a general theory. Our knowledge of politics at all levels of interaction is even more fragmentary, as is our understanding of how other disciplines can augment this knowledge.

There is more than one way to skin a cat, and clever political scientists have devised alternative strategies for theorizing about international relations. The most obvious move is to ignore the need to understand politics holistically and to assume that patterns of international behavior can be studied independently of what transpires at other levels of interaction.